The Sri Lankan government today announced it was ending the use of air and artillery strikes in its war with the Tamil Tigers, after weeks of denying that it was using such weapons.

As international pressure for an end to the fighting mounted, the government issued a statement in which it said combat operations had reached their conclusion and that it would now concentrate on rescuing civilians.

"Our security forces have been instructed to end the use of heavy caliber guns, combat aircraft and aerial weapons which could cause civilian casualties," it said.

The statement appeared to contradict previous claims by the military that it had not been using heavy weapons.

The United Nations says more than 6,000 civilians have died in the fighting since January. Many of the dead and injured have suffered blast injuries. A doctor working in the no-fire zone claimed yesterday that there had been a series of air strikes on the area during the day.

A military spokesman contacted by the Guardian today continued to insist that air strikes and artillery had not been directed at areas in which civilians had taken shelter.

But Brigadier Udaya Nanayakkara confirmed that those weapons had been used against the Tamil Tigers – or Liberation Tigers of Tamil Eelam (LTTE) – during the fighting in recent weeks. "We have been using them outside the safety zone," he said.

There were fresh reports of fighting inside the no-fire zone this morning and reports circulating among diplomats in the capital, Colombo, yesterday described a number of Sri Lankan air strikes during the day on positions held by the LTTE.

The Tamilnet website, which carries LTTE statements, claimed that fighter jets from the Sri Lankan air force had bombed the area.

A doctor working in the no-fire zone, Thangamutha Sathiyamoorthy, said there had been nine air strikes on the Mullivaikal south area during the day, the first at 7.30pm and the last at 2.05pm.

Sathiyamoorthy said 154 civilians had been admitted to the temporary hospital at Mullivaikal on Saturday with injuries sustained in air strikes, shelling and attacks by gun boats, and 15 had died. He said another 84 were admitted yesterday and 14 had died.

The government has accused Sathiyamoorthy of acting as a mouthpiece for the LTTE.

It is not possible to verify any of the reports because independent access to the area has been denied by the government.

The Sri Lankan government yesterday flatly rejected a ceasefire declaration by the cornered Tamil Tigers and said fighting would continue until the rebels laid down their weapons and surrendered.

The government dismissed the ceasefire as a "gimmick" and said fighting was continuing around the no-fire zone, in which as many as 150,000 civilians are still believed to be trapped. The government disputes that figure.

According to UN officials, there was no sign of the exodus of civilians from the no-fire zone which would be expected if the Tamil Tigers had stopped fighting.

Diplomatic pressure has been mounting on Colombo, with the British foreign minister, David Miliband, due to arrive in the country on Wednesday, along with his French and Swedish counterparts.

Sri Lankan government officials have made clear that they regard the interventions as unnecessary and unwelcome.

The unilateral ceasefire declaration came as Sri Lankan forces continued to close in on a small number of LTTE rebels who are fighting for their lives in a tiny strip of coastline estimated to be no larger than 10 sq km.

In a statement, the LTTE said: "In the face of an unprecedented humanitarian crisis and in response to the calls made by the UN, EU, the governments of India and others, the Liberation Tigers of Tamil Eelam has announced a unilateral ceasefire."

The defence secretary, Gotabaya Rajapaksa, described the offer as "a joke". "They were not fighting with us, they were running from us. There is no need of a ceasefire. They must surrender. That is it."

Nanayakkara said the LTTE had taken advantage of a previous ceasefire, announced by the government to mark the Sri Lankan new year, to fortify its defences.

"They want to use a ceasefire to get organised and to get some breathing space. We are not going to give in to the tricks of the LTTE," he said.

The military said 23 LTTE cadres surrendered to the advancing troops yesterday.

A government spokesman dismissed the ceasefire as "futile". "It is rather late in the day. The endgame is very much on. This is just a gimmick."

UN officials reacted warily to the ceasefire declaration. "Like a unilateral declaration of a no-fire zone, I don't think it means a lot unless it is agreed with the other party," one official said.

Another described it as a "strategic ploy" timed to coincide with the arrival of the UN's top humanitarian official, John Holmes, in Sri Lanka.

Holmes arrived on Saturday hoping to persuade the government to open the war zone to humanitarian groups. Aid workers have been barred from the region since fighting escalated in September.

He was due to travel to Vavuniya today to inspect the camps where tens of thousands of Tamil civilians have been interned after escaping from the fighting.

The Sri Lankan government said close to 200,000 people were either inside the camps it has set up outside the no-fire zone or were making their way from the combat area.